"These are results that are warning bells and there is the persistent missing voice of women where it matters most."

Mlambo-Ngucka said the new data was "quite troubling" and the failure to achieve progress in women's representation in politics raised questions about democracy.

The global average of women in national parliaments increased only slightly from 22.6 percent in 2015 to 23.3 percent last year, according to the data from the Inter-Parliamentary Union (IPU) and UN Women.

"Power is still firmly in men's hands," said IPU Secretary-General Martin Chungong, who said the failure to achieve progress was due to a lack of political will.

Bulgaria, France, Nicaragua, Sweden and Canada have achieved gender parity in government, with women holding at least half of all ministerial posts.

Most women ministers in the world hold the environment, energy or natural resources portfolios, followed closely by social affairs.

Finland and Cape Verde, which have had high rates of women ministers, dropped significantly.

Women are also losing ground in Africa, but there were big gains for women in elections in Pacific island-states.

The data was released during the Commission on the Status of Women, a two-week UN conference aimed at taking stock of progress toward gender equality.